New finding may explain heat loss in fusion reactors

January 21, 2016
by David L. Chandler

One of the biggest obstacles to making fusion power practical—and realizing its promise of virtually limitless and relatively clean energy—has been that computer models have been unable to predict how the hot, electrically charged gas inside a fusion reactor behaves under the intense heat and pressure required to make atoms stick together.

The key to making fusion work—that is, getting atoms of a heavy form of hydrogen called deuterium to stick together to form helium, releasing a huge amount of energy in the process—is to maintain a sufficiently high temperature and pressure to enable the atoms overcome their resistance to each other. But various kinds of turbulence can stir up this hot soup of particles and dissipate some of the intense heat, and a major problem has been to understand and predict exactly how this turbulence works, and thus how to overcome it.

A long-standing discrepancy between predictions and observed results in test reactors has been called "the great unsolved problem" in understanding the turbulence that leads to a loss of heat in fusion reactors. Solving this discrepancy is critical for predicting the performance of new fusion reactors such as the huge international collaborative project called ITER, under construction in France.

Now, researchers at MIT's Plasma Science and Fusion Center, in collaboration with others at the University of California at San Diego, General Atomics, and the Princeton Plasma Physics Laboratory, say that they have found the key. In a result so surprising that the researchers themselves found it hard to believe their own results at first, it turns out that interactions between turbulence at the tiniest scale, that of electrons, and turbulence at a scale 60 times larger, that of ions, can account for the mysterious mismatch between theory and experimental results.

For the first time, researchers show two types of turbulence within plasma that cause significant heat loss. Solving this problem could take the world a step closer to fusion power. Credit: Melanie Gonick/MIT (plasma simulations and Alcator C-mod footage courtesy of General Atomics and MIT PSFC)

The new findings are detailed in a pair of papers published in the journals Nuclear Fusion and AIP Physics of Plasmas, by MIT research scientist Nathan Howard, doctoral student Juan Ruiz Ruiz, Cecil and Ida Green Associate Professor in Engineering Anne White, and 12 collaborators.

"I'm extremely surprised" by the new results, White says. She adds that it took a thorough examination of the detailed results of computer simulations, along with matching experimental observations, to show that the counterintuitive result was real.

Persisting eddies

The expectation by physicists for more than a decade had been that turbulence associated with ions (atoms with an electric charge) was so much larger than turbulence caused by electrons—nearly two orders of magnitude smaller—that the latter would be completely smeared out by the much larger eddies. And even if the smaller eddies survived the larger-scale disruptions, the conventional thinking went, these electron-scale whirls would be so much smaller that their effects would be negligible.

For the first time, simulations of realistic plasmas have demonstrated the coexistence of large turbulent eddies and smaller scale, finger-like turbulent structures known as "streamers."

The new findings show that this conventional wisdom was wrong on both counts. The two scales of turbulence do indeed coexist, the researchers found, and they interact with each other so strongly that it's impossible to understand their effects without including both kinds in any simulations.

However, it requires prodigious amounts of computer time to run simulations that encompass such widely disparate scales, explains Howard, who is the lead author on the paper detailing these simulations. Accomplishing each simulation required 15 million hours of computation, carried out by 17,000 processors over a period of 37 days at the National Energy Research Scientific Computing Center—making this team the biggest user of that facility for the year. Using an ordinary MacBook Pro to run the full set of six simulations that the team carried out, Howard estimates, would have taken 3,000 years.

But the results were clear, and startling. Far from being eliminated by the larger-scale turbulence, the tiny eddies produced by electrons continue to be clearly visible in the results, stretched out into long ribbons that wind around the donut-shaped vacuum chamber that characterizes a tokamak fusion reactor. Despite the temperature of 100 million degrees Celsius inside the plasma, these ribbon-like eddies persist for long enough to influence how heat gets dissipated from the swirling mass—a determining factor in how much fusion can actually take place inside the reactor.

Previously, scientists had thought that simply simulating turbulence separately at the two different size scales and adding the results together would give a close enough approximation, but they kept finding discrepancies between those predictions and the actual results seen in test reactors. The new multiscale simulation, Howard says, matches the real results much more accurately. Now, researchers at General Atomics are taking these new results and using them to develop a simplified, streamlined simulation that could be run on an ordinary laptop computer, Howard says.

Video of plasma in the Alcator C-Mod reactor.

Independent evidence

In addition to the theoretical simulations, MIT graduate student Ruiz Ruiz, lead author of the second paper, has analyzed a series of experiments at the Princeton Plasma Physics Laboratory, which provided direct evidence of electron-scale turbulence that supports the new simulations. The results offer clear, independent evidence that the electron-scale turbulence really does play an important role, and they show that this is a general phenomenon, not one specific to a particular reactor design.

That's because Howard's simulations were based on MIT's Alcator C-Mod tokamak reactor, whereas Ruiz Ruiz's results were from a different type of reactor called the National Spherical Torus Experiment, which has a significantly different configuration.

Understanding the details of these different mechanisms of turbulence has been "an outstanding challenge" in the field of fusion research, White says, and these new findings could greatly improve the understanding of what's really going on inside the 10 tokamak research reactors that exist around the world, as well as in future experimental reactors under construction or planning.

"The evidence from both of these papers, that electron energy transport in tokamaks has a significant contribution from both ion and electron-scale turbulence and that multiscale simulations are needed to predict the transport, is profoundly important," says Gary Staebler, a researcher at General Atomics who was not involved in this work. "Both of these papers are very high quality," he adds. "The execution and analysis of the experiments is first class."

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Look at how much difficulty theorists have in simulating plasma EVEN WHEN THEY HAVE A LABORATORY TO TEST THEIR ASSUMPTIONS ABOUT IT.

Now, consider the obvious implication -- and the claim made by Hannes Alfven many years ago about COSMIC plasma -- that the attempts, to date, to simulate the universe's most dominant state of matter in astrophysics and cosmology IS JUST AS WRONG, and probably all the more since there is not the convenience of a laboratory to provide instantaneous feedback on the mistakes.

Well, they have no laboratory setup to test self-sustained nuclear fusion. That's what they are looking for.

They are trying to initiate fusion based on the solar model, which is theoretical. In other words this is how we think the sun works to produce fusion so we will try to duplicate what we think is happening. The inability to do this isn't because they are "missing something" in the Tokamek design so much as the theory of how the sun works is wrong. As all observational evidence that comes in continues to show.

So the genius answer to "the great unsolved problem" was to check your assumptions!? I hope the real answer is that the simulations are so complex that we didn't have the technology until now to do them properly and discover this complex interaction, not that we were too stupid to check our over-simplified assumptions which ignored the effect of half the charged particles in the plasma.

Hi Eikka. :) Pity to see personal animosity persist into this New Year of discovery and understanding.

Anyhow..

gkam said:

We do not need unlimited energy produced by a few powerful people or agencies. We need diversification and distribution of generation assets for reliability, cost savings, and freedom from dominance.

And Eikka replied:

If you ever found a cornucopia, you'd smash it to pieces on the logic that there's just one of them. Even while you were starving.

I suspect gkam's response to that sarcastic retort from you, Eikka, might be something along the lines of "Those who control that "cornucopia" controls the rest."

Eikka, I gather gkam's beef with big corporations controlling centralized sources of 'necessities' is a recipe for much political/financial/criminal monopoly abuse. That is what we're trying to get away from if (1) energy-poverty is to be reduced among the many not on such grids, and (2) energy-savings/independence to be increased. :)

Gkams beef? Gkam enjoys hopping around like a trained monkey screeching 70s slogans and pretending he is impressing people.

Gkam could care less about the issues. If he did he would actually be discussing them.

There are new and more effective ways of producing fusion energy being discovered all the time. Tokamaks are obviously being developed to teach us how to store large quantities of materials in the plasma state.

In the near future we will begin producing materials which can only be stored in such a state, like antimatter. Closed bottles such as tokamaks are the only known way of doing this at present.

The prospect of unlimited energy is a rather harmless cover story.

One thing we may want to know is how to store plasmas at above fusion temps while suppressing the tendency to fuse. This might explain the lack of 'progress' to some extent.

There are new and more effective ways of producing fusion energy being discovered all the time. Tokamaks are obviously being developed to teach us how to store large quantities of materials in the plasma state.

In the near future we will begin producing materials which can only be stored in such a state, like antimatter. Closed bottles such as tokamaks are the only known way of doing this at present.

One thing we may want to know is how to store plasmas at above fusion temps while suppressing the tendency to fuse. This might explain the lack of 'progress' to some extent.

Hmmmm..... seems you are hinting at something? Like, you might know of why fusion doesn't happen the way they are trying?

You are aware that fusion has already been initiated that way in experimental setups? The 'only' thing missing is to find a way to keep it going in a stable manner. So the theory is correct because it is working.

So the genius answer to "the great unsolved problem" was to check your assumptions!?

It always is. But you must understand that the number of points where one can look for clues is near infinite. Science is not at an end. There's still a LOT to be discovered. And it gets increasingly hard the further into the details you have to look for an answer.

We do not need unlimited energy produced by a few powerful people or agencies.

We need it for space exploration. Some power hungry branches of industry could also benefit. It's also a vastly preferrable (to natural gas/fission) intermediary fix to the energy problem.

Eikka, I gather gkam's beef with big corporations controlling centralized sources of 'necessities' is a recipe for much political/financial/criminal monopoly abuse.

Gkam just doesn't want to understand that the availability of fusion power doesn't make all the renewable power technology go away. If you want to, you can still build a wind turbine and a solar panel and be independent.

The issue here is, that those technologies are not actually technically, economically and socially viable without huge limitations and re-structuring of society, and have to be forced into use by some sort of "collective" (read: centralized) authority, and that involves denying every other possible solution to the problem of our lack of clean energy sources.

Whether it's fission, fusion, synthetic hydrocarbons... anything that is "too good" has to be resisted because it means gkam and other people who think like him don't get to grab social power in their bid to "help" everyone.

Basically, even when you are a "power to the people" type, you fail to see that you yourself don't actually represent the whole of the people. Your opinions and preferences are not universal, so don't speak with the mouths of the many.

And the irony is that the renewable sources and the distribution grids that make them possible are also owned by big corporations, because they simply don't work on a small local scale that you could build yourself. You're utterly dependent on a huge multinational corporation to manufacture you the power lines and solar panels and the batteries to have a functioning "distributed energy infrastructure", which then has to be supervised and controlled and rationed by a central authority or else it runs into chaos and burns down.

It's the great illusion of people who think they're independent because they can go to a hardware store to buy a solar panel, made in China.

It's also a matter of difference in opinion about human destiny and direction in the world.

Gkam says "we don't need unlimited power", or rather "we should not have unlimited power", which is a moral judgement. It's a statement that humanity has to deliberately limit itself into a zero-sum game where the prosperity of one person is automatically a loss to another person.

The problem with that is that you automatically become a tyrant. You end up making an arbitrary limit for the entire humanity, where everyone has to stop. Go to the moon, but no further. Travel 10 miles a day, eat 2000 calories, give birth to 2.1 babies, live in a house with three rooms - never more - to give an example.

That is your place as a human being, and our place as the human species, dictated by one singularily wise mind known as "gkam" who says that we should not have unlimited power.

The fact of the matter is that the person who owns the cornucopia doesn't need anything from anyone else.

They do not need to control the masses for any purpose because all their material wishes are fulfilled - why would you need to enslave the people if you have all the power in the world anyways? Just make a robot to do your bidding.

The only fear of the person who has the cornucopia is that other people would try to take it away from him, but that is easily solved: just pull another cornucopia out of the first one and give it to the rest.

Peace through prosperity. When I have a fusion powerplant and you have a fusion powerplant, we don't need to fight for energy.

In fact we have only theoretical model for the energy generation processes in the stars which can not be checked with direct observation or experiments. For this processes scientists think that is needed enough concentration and kinetic energy for the particles. But if the structure of the vacuum of space which define the behavior and interaction between elementary particles locally and globally is not programmed accordingly, the fusion reaction will never happen. Stars are working thanks to different physical laws.

Anyway your argument was that solar fusion can not be directly observed.Note that you don't even know the difference between fusion and fission and still dare to criticise those who do. BUT, the solar neutrinos resulting from it are directly observed.Now admit that you are wrong. W R O N G.

The point is, centralized generation/grids are vulnerable to disastrous failures that put whole regions into blackout for days/weeks. Also poorer people far from 'profitable' grid left in the lurch, or exploitatively exorbitant charges to extend grid power to them/excludes them. Also during early planning/development/implementation, all centralized generators/grids had massive govt (society/public) subsidies/assistance etc, so renewables deserve same treatment; moreover, the planning-building-rollout phases for centralized systems much longer/expensive, whereas local as-needed renewables generation/grid less time/cost and reaches those too poor/excluded from centralized grids; and also such local self-reliance makes people less exploitable by politicians and monopolists/mafia who control both govt and means of generation/distribution.

Re plasma fusion power/stream: too costly; too late (decades); too hard to control for more than microseconds; etc. See now? :)

In fact we have only theoretical model for the energy generation processes in the stars which can not be checked with direct observation or experiments. For this processes scientists think that is needed enough concentration and kinetic energy for the particles. But if the structure of the vacuum of space which define the behavior and interaction between elementary particles locally and globally is not programmed accordingly, the fusion reaction will never happen. Stars are working thanks to different physical laws.

And for man to have access to this knowledge frightens you... Hmmm, interesting...Anyway, the simple issue is that fusion doesn't like an artificial "containment" and so feeds back on itself. These guys have just figured out that it does that....

Hi Eikka. :)The point is, centralized generation/grids are vulnerable to disastrous failures that put whole regions into blackout for days/weeks.

Eerily similar to what we have now, eh?

Also poorer people far from 'profitable' grid left in the lurch, or exploitatively exorbitant charges to extend grid power to them/excludes them. etc.

Didn't happen to us out on a farm in the middle of an empty (then, at least) North Dakota...

.., massive govt (society/public) subsidies/assistance etc, so renewables deserve same treatment ... whereas local as-needed renewables generation/grid less time/cost and reaches those too poor/excluded from centralized grids; and also such local self-reliance makes people less exploitable by politicians and monopolists/mafia who control both govt and means of generation/distribution.

So your definition of "self reliance" is to follow the example of what "monopolist/mafia" did?You wish to "socialize" huge investments by others...?

@vikoWe can observe neutrinos from solar fusion directly.This contradicts your assertion "the energy generation processes in the stars which can not be checked with direct observation or experiments".Rather than admitting you are talking nonsense, which is your religion after all, you bring up neutrons. It is still unclear why, except as a diversion.

Also poorer people far from 'profitable' grid left in the lurch, or exploitatively exorbitant charges to extend grid power to them/excludes them. etc.

Didn't happen to us out on a farm in the middle of an empty (then, at least) North Dakota...

If you're lucky enough to be in a place where the long-distance grid lines run reasonable close enough to extend easily/cost-effectively/profitably to your place, then that is good luck for you. Masses of people around the world not in that fortunate 'proximity' position, especially in India, Africa, Australia etc.

massive govt (society/public) subsidies/assistance etc, so renewables deserve same treatment ... whereas local as-needed renewables generation/grid less time/cost and reaches those too poor/excluded from centralized grids; and also such local self-reliance makes people less exploitable by politicians/monopolists/mafia who control both govt and means of generation/distribution

So your definition of "self reliance" is to follow the example of what "monopolist/mafia" did? You wish to "socialize" huge investments by others

You've conflated two issues into one there.

1)Mafia/centralized control/exploitation/monopoly/abuses etc is to do with precisely that, exploitative/criminal control/monopoly excluding/denying/exploiting those 'not profitable/exploitable' enough to extend grid to without exhorbitant charges.

2)Renewables subsidies is matter of equal treatment with fossil generators/industry who got such to assist/expedite implementation.

Renewables subsidies is matter of equal treatment with fossil generators/industry who got such to assist/expedite implementation.ok? :)

I understand the sentiment. However, isn't that the antithesis of "self-reliance"?

Not 'sentiment'. It's recognition of the financial/developmental/implementational trajectory all major undertakings of national importance/reliance go through. In the age of fossils, it was so. In this new age of renewables, it is also so. Equal treatment for the national benefit, not just individual independence. Fortunately, with the renewables options, the two are closely aligned and make the reasons for going renewables even more attractive; both to individuals/towns previously excluded from current fossil/centralized generation/distribution grids; and to national wealth/health/future capabilities and resistance to disastrous outages due to affected centralized fossil power systems/grids.

I agree with Whydening-Skippy. But I also agree with you too me. Renewables should be subsidized, a lot. It's like investing in the future. Building roads and railways is subsidies, but we need the things built. It don't matter that they cost more than the gas (which I hate the most) or coal or nuclear. The cost is not just in the building it, you also got figure in the cost of the future quality of life too. Getting rid of the gas wells and oil wells and coal mines needs to be subsidized.

Not 'sentiment'. It's recognition of the financial/developmental/implementational trajectory all major undertakings of national importance/reliance go through. In the age of fossils, it was so. In this new age of renewables, it is also so. Equal treatment for the national benefit, not just individual independence.

I could be wrong, but I thought in the early 20th century, "subsidies" for building of the fossil fuels infrastructure were more from tax breaks (often obscene) than actual cash.

Fortunately, with the renewables options, the two are closely aligned and make the reasons for going renewables even more attractive; ... and to national wealth/health/future capabilities and resistance to disastrous outages due to affected centralized fossil power systems/grids.

Still requires sizeable installations (to replace the fossil fuel infrastructure) and a lot of private outlay (which many are wont to provide). (cont)

The point is, centralized generation/grids are vulnerable to disastrous failures that put whole regions into blackout for days/weeks.

You and many don't understand what centralization/decentralization even means in reality.

A single homestead uses ~2 kW, a shopping mall may use 200 kW, a factory can use 2,000 kW and more, and it's simply not possible to produce this kind of power in a little by little in a decentralized fashion. It requires a steady supply from an efficient grid.

In the scale of societies, individual homes use up 15-20% of all the electricity, and industry and commerce uses up 80%, and then there's double that in heat, and transportation to add. In that scale, renewable power is no longer "decentralized" - it works as a single huge unit that responds to sunrise and sunset as one, or a 500 mile wide weather front in the case of wind turbines.

A home isn't just the energy it uses directly. To have a home, you use lots more energy outside of it.

local self-reliance makes people less exploitable by politicians and monopolists/mafia who control both govt and means of generation/distribution.

There is no local self-reliance with renewables because they depend on the grid at large to smooth out the intermittency over large distances. A geographical timezone where e.g. the sun is up or down on the same hour is vast - a thousand miles east to west.

Only at the very smallest scale can you rely on a bunch of very expensive batteries, and rationing your power, and getting your heating fuel by other means to actually remain off-the-grid. Still you are not self-reliant because you have to obtain the batteries and the solar panels and other electronics, and that is again subject to control by the "mafia".

A town with a bunch of solar panels and wind turbines is not practically self-reliant. Even a county sized unit doesn't work completely independently with renewables. A state size unit may be, with difficulty.

Eikka's World is absolute, no variations, everybody has the same feelings impulses, the same actions, the same character.

You project your own attitudes on me, mr. "California is the entire world".

If somebody wants to wreak havoc or disaster because he is angry, he can do it with his unlimited power, and Eikka thinks that is okay. Who would YOU trust with that?

So you do want a central control to limit how much energy people can have after all. Why didn't you say so in the first place?

Who would you trust with -that- power?

You have a child's understanding of the issue. You hang on to the idea of "unlimited power" literally almost as if people would actually become Clark Kent the Superman, and then go around punching office buildings down. Well, if everyone's superman then punch him back. You got the same power.

We're already at a point where we can just nuke each other to pieces, and we haven't even gotten to the part with unlimited energy.

Unfortunately that is not what ends up happening with subsidies. They end up targeted wrong and overly generous, with loopholes and other faults that enable private corporations to simply milk money out of the public without giving them anything worthwhile in return.

By the time the general infrastructure and technology has been evolved to deal with renewable power in a sustainable manner, the current crop of wind turbines and solar panels etc. have been delegated to the landfill, having provided nothing but a hinderance on the effort by draining away investments from actual research and development.

It's also disingenous to compare energy investments from 50-100 years ago to energy subsidies today and call them the same. Today's energy subsidies aren't investments in renewable energy, they're just directly paying private companies to make incredibly expensive electricity.

It's curious how people seem to completely lack any sense of scale on the renewables issue.

For example, people like gkam may on one hand argue that renewable energy already works in a "decentralized" fashion on the local level, without providing details on how it is going to work, what's it going to cost, who's going to pay it etc. etc. Then when pushed they may say like "well we can build pumped hydroelectricity", which is not a local distributed means but a huge artifical lake that costs billions of dollars, or "we can buy Tesla Powerwalls" which is again another billion dollar industry controlled by one man, and can't actually make enough batteries for everyone.

It's like the old joke about a mathematician who woke up in the middle of the night with flames licking up the wall of his room. He saw a glass of water on his bedside table and said "The solution exists.", and went back to sleep.

It's curious how people seem to completely lack any sense of scale on the renewables issue.

Study after study has shown that we can run our world on renewables. Here is just one http://www.skepti...wer.html There are plenty of examples in the world (try Denmark, or Portugal, or Costa Rica) - that show us that renewables can be scaled up. The time frame is of course a big question - we are probably looking at a 50 to 100 year transition.

Eikka

and that involves denying every other possible solution to the problem of our lack of clean energy sources.

Total rubbish. Why do you comment when you have no understanding of the world? Please answer that question. We are currently funding the development of next gen nukes. http://www.energy...reactors Must be scary under that desk Eikka.

You are aware that fusion has already been initiated that way in experimental setups? The 'only' thing missing is to find a way to keep it going in a stable manner. So the theory is correct because it is working.

As usual you take the PR campaign route and claim that because one part of a theory is correct the rest will eventually just fall into place. Yes, they can and do fuse matter in Tokameks...how about you look up the MOST efficient one and see what the energy deficit is?

Continuously trying to modify an existing design will never work if the assumptions behind the method by which it works are incorrect....even if every single bug is worked out.

How long have Tokameks been around again?

We can observe neutrinos from solar fusion directly.

Oh really? Define "directly".

You also confuse neutrons with neutrinos.

You confuse "directly" with an interaction through which their presence is inferred.

"It's curious how people seem to completely lack any sense of scale on the renewables issue."-----------------------------------

Yes, . . we were wondering about you.

Eikka, you are new to this field, it seems. Do you really think your fears are unknown to others, who have already taken care of them for you? Do you really think you have thought of problems with technologies which others who work with have not?

It's why they built every single one....remember? Still missing that number on energy deficit.

True. However there's not a single indication that the assumptions are incorrect.

How about the lack of an energy surplus from fusion in these reactors? In other words, based on the assumptions, and 60 years of continuous engineering refinements, were still 10 years away....I would call that a single indication.

Huh? Your brain uses electrical impulses to interpret the effect of photons impacting on your retina. Do you doubt photons?

That is direct detection, not to mention the supporting evidence of color absorption. What is the direct detection instrument for neutrinos?

Be careful, you seem a bit confused about the meaning of "direct detection". At least you aren't alone.

"For example, people like gkam may on one hand argue that renewable energy already works in a "decentralized" fashion on the local level, without providing details on how it is going to work, what's it going to cost, who's going to pay it etc. etc."-----------------------------------Attention, Eikka and other technological deniers:

And on the local levels, my utility is integrating my PV into their distribution system, along with that of my neighbors, some of whom also have plug-in vehicles. Perhaps you do not understand we in California have been integrating different sources into our grid for over 40 years.

...I thought in the early 20th century, "subsidies" for building of the fossil fuels infrastructure were more from tax breaks...

Also land grants, rail service discounts/construction subsidies, guaranteed market from govt contracts and captive consumer base allowed monopolistic exploitation/exclusion as previous discussed, etc etc on top of what you already mentioned.

Still requires sizeable installations)

That is where subsidies, tax breaks etc which the fossils received during formative years (and still) should also be offered to renewables to encourage expeditious development/implementation in many hybrid situations of private-public initiatives.